P-I Focus: We need to get out of the clouds on issue of warming

NATHAN MANTUA, SPECIAL TO THE SEATTLE POST-INTELLIGENCER

Published 10:00 pm, Saturday, May 24, 2003

Life in the Northwest is shaped by the rhythms of climate. The evidence is all around us. The wet and mossy evergreen forests that tower west of the Cascade Range and the sage-steppe, orchards and rolling wheat fields of the dry and sunny area east of the mountains illustrate our region's amazing contrast in landscapes, flora and fauna.

Each year we see a hefty winter snowpack build in our mountains and witness the spring melt sending water surging into our largest rivers. The ongoing cycle brings the spring blooms of Skagit Valley tulips, the summer cherries of the Yakima Valley, the fall apple crops of Wenatchee and the fall and winter return of tens of thousands of coho and chum salmon to the streams of Puget Sound.

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Just like the natural systems that make the region unique, human-built systems have evolved in ways that work with the climate of this place. We have built an extensive infrastructure to tap into our renewable resources. In particular, hydropower dams and storage reservoirs were designed to take advantage of the mountain snowpack and the resulting abundance of spring and summer runoff. These provide inexpensive and abundant electricity for people and industry and water for irrigators, industry and urban centers.

Those who built the dams, reservoirs and irrigation canals may not have realized it at the time, but they were basing some of their decisions on long-range climate forecasts. Did they consult The Old Farmer's Almanac?

Perhaps, but a more typical story is that those politicians, planners and engineers assumed the climate of the future for which they were building would look like the climate of the past. To their credit, most planners sifted the historical climate record to identify the most challenging conditions their systems might face, whether an extreme winter flood or a prolonged drought.

Plans were (and still are) written so that water and hydropower systems will work if the historic worst-case climate scenario happens again.

Recent climate extremes produced tangible reminders that many facets of Northwest life remain sensitive to the push and pull of climate change. In the winter of 1998-99, the region experienced one of the wettest periods in memory. Mount Baker, near Bellingham, set a record for the greatest annual snowfall ever recorded anywhere, with a remarkable total just shy of 100 feet. The spring and summer of 1999 saw a wide abundance of runoff and hydropower production in the region.

The winds and ocean currents of 1998-99 also brought significant cooling to the coastal ocean environment, with upper ocean temperatures dropping up to 8 degrees Fahrenheit from the exceptionally warm winter of 1997-98. That cooling marked the beginning of a four-year run of much more productive ocean conditions for many stocks of Northwest coho and chinook salmon that had been severely depleted in the mid-'90s.

But just two years later, our climate swung to the other extreme. The winter of 2000-01 brought the region one of the driest "wet" seasons in a century.

Late-season snowpack in the Cascades and the snowmelt runoff in the Columbia Basin were only about 60 percent of the long-term average. Irrigation flows for some farmers were severely restricted, and stream-flow targets aimed at protecting migrating salmon were frequently missed.

To make matters worse, the California energy markets were spinning wildly out of control, ultimately spiking the price of electricity all along the West Coast -- a convergence of climatic and socioeconomic events that will affect electrical ratepayers for years to come.

El Niño and La Niña get a lot of media attention around here, even though those labels apply to changes in winds, ocean temperatures and rainfall patterns in the tropical Pacific Ocean. Yet those two phenomena deserve our attention because they shift tropical rainfall patterns in ways that disturb wind and weather patterns over the northern Pacific and North America.

El Niño typically favors a relatively warm and dry Northwest winter and a yearlong warming of our coastal ocean. Those who ski or fish for salmon ought to be fans of La Niña, because that typically favors a cool and wet Northwest winter and a salmon-friendly, yearlong cooling of our coastal ocean. Natural tropical swings between El Niño and La Niña typically get started in our summer, then develop through the fall and winter months before fading away the next spring. An extensive network of buoys, ships and satellites provides us with an accurate picture of the status of El Niño or La Niña several months before our winter begins.

When we look back at our region's climate in the 20th century, we also find 20- to 30-year eras of climate conditions that strayed from the long-term average.

Mostly cool-and-wet years were the rule from 1946 through 1976, while warm-and-dry periods prevailed from 1925 through 1945 and again from 1977 through 1998. Part of this longer-term climate variability has been associated with a long-lived El Niñolike climate pattern called the Pacific Decadal Oscillation.

After 1976, that phenomenon brought an increase of a degree or two in the cold half of the year and about a 10 percent decline in average annual precipitation. Because of the warmer and drier conditions, spring snowpack at Paradise ranger station on Mount Rainer was typically 20 percent (about 44 inches) lower than it was during the cool periods of the '50s through early '70s.

Moisture in our forests, which varies with temperature, precipitation and snowpack, is thought to be a key climate link to past changes in forest regeneration and the frequency and intensity of large Northwest forest fires.

Low snowpack in the '80s and '90s allowed subalpine fir trees to invade wildflower meadows on the east side on Mount Rainier. The history of large forest fires in the Northwest also parallels the changes in the Pacific Decadal Oscillation, with large fire years concentrated in the warm-and-dry periods of the '30s, '80s and '90s, and relatively quiet fire eras in the late '40s through mid-'70s.

Climate effects on ecosystems can be seen in the ocean as well as on land. When the Pacific Decadal Oscillation shifted from cool to warm conditions in the late '70s, ocean temperatures warmed by 1 to 2 degrees, and there were major shifts in coastal ocean food webs. The abundance of cold-water forage fish and plankton dropped, but numbers of warm-water fish such as mackerel, hake and sardines increased. Ocean survival rates for many Northwest chinook and coho salmon populations reached historic lows in the warm-ocean years of the early to late '90s, and the persistently low return rates contributed to large population declines for already depleted stocks.

Century-long trends account for another important part of the long-term changes in 20th-century climate. The warming observed globally during the past century, which averaged about 1 degree, was mirrored by Northwest warming of about 1.5 degrees. Precipitation increased by 10 percent to 30 percent across much of the region. Since the 1950s, the warming climate has eroded our annual snowpack, especially at elevations below 6,000 feet.

Because of human-caused increases in atmospheric greenhouse gases caused by burning fossil fuels and converting forests to agricultural lands, an overwhelming majority of scientists expect 21st-century climate to be substantially warmer than that of the recent past. Climate models are providing some clues about what will happen because of the accumulation of greenhouse gases. State-of-the-art climate models suggest additional year-round increases in regional temperatures of 2.5 to 4 degrees for the 2020s, and 3 to 6 degrees for the 2040s. Most climate models also project modest increases in winter precipitation (typically around 10 percent).

Some of the consequences of a warmer and wetter Northwest climate are clear.

Rising snow lines, a declining snowpack, stream-flow increases in winter and declines in summer are always observed during an unusually warm Northwest winter and spring. Our present climatic course promises to transform the "unusual" of our experience to the "normal" of our future.

Warming-induced changes in the region's snowpack and stream flow will bring new challenges to our water and power systems, and even more problems to wild salmon that inhabit already degraded streams. Reduced snowpack likely will allow west-side forests to expand to higher altitudes, yet warmer temperatures may increase drought stress in low-elevation forests in ways that increase fire, disease and pest outbreaks.

Whether you farm or garden, work or play in the mountains, forests, streams, lakes, estuaries or ocean, your experience always will be shaped by climate. A climatic warming of a few degrees will change life as we know it in the Northwest; residents and regional planners can take that forecast to the bank.